(a) Field of the Invention
The present invention relates to a novel hydrazone compound which is usable as a charge transfer material and is represented by the general formula I: ##STR2## (wherein R is hydrogen, an alkyl group, an alkoxy group or a dialkylamino groups, and n is an integer of 1 to 3), a manufacturing process for the compound and its application in electrophotographic elements.
(b) Description of the Prior Art
Inorganic substances such as selenium, cadmium sulfide, zinc oxide, etc. have hitherto been employed as photoconductive materials for electrophotographic elements used in electrophotographic processes. In this context, it is to be noted that the term "electrophotographic process" referred to herein generally denotes one of the image forming methods which comprises the steps of first electrifying an electrophotographic element in the dark, for instance with corona discharge or the like, then subjecting the element to imagewise exposure for selectively dissipating the charge from only the light struck portions of the element, thereby forming a latent image, and rendering the latent image visible by virtue of a developing process utilizing an electroscopic fine powder comprising a coloring agent called a toner, such as a dye, pigment or the like and a binder resin such as a high molecular weight substance or the like, thereby forming a visible image. The element adapted for the above-mentioned electrophotographic process is required to have the following fundamental characteristics: (1) chargeability to a suitable potential in the dark, (2) low charge-dissipation in the dark, and (3) rapid dischargeability on irradiation of light. The hitherto utilized inorganic substances as enumerated above surely possess a number of merits but at the same time have various inherent demerits. In order to remove these inherent drawbacks, in recent years there have been proposed electrophotographic elements employing various kinds of organic substances, and some of these are now put to practical use. It is known that an electrophotographic element comprising a material capable of generating a charge carrier on absorption of light (which will be referred to as a charge carrier generating material hereinafter) and a material capable of accepting as well as transferring the charge carrier thus generated (which will be referred to as a charge transfer substance hereinafter) can exhibit a hitherto unexperienced high sensitivity since it can utilize a wide variety of materials suitable for each of the charge carrier generating and transferring functions as compared with an electrophotographic element wherein one and the same material is designed to generate a charge carrier as well as transfer same. The materials suitably used in the electrophotographic element of this sort are required to meet the following requirements: in the case of the charge carrier generating substance, it should generate a charge carrier on absorption of a desired light; it should generate a charge carrier with a high efficiency; and it should be readily processed in the preparation of the electrophotographic element and the like. The charge transfer substance should easily accept the charge carrier from the charge carrier generating substance; it should transfer the charge swiftly; it should exhibit no absorption in the photosensitive region of the charge carrier generating material and the like. In this connection, it should be particularly taken into consideration that the charge carrier generating material and the charge transfer material suitable therefor are inseparably related to each other. In other words, when the combination of the charge carrier generating material and the charge transfer material is unfit, it results in that a satisfactory charge potential can not be obtained in the dark, the dissipation of charge on irradiation of light is not effected satisfactorily and consequently the image to be obtained is low in image density and the background is stained. Generally speaking, there is noted such a tendency that the material which exhibits a high charge potential in the dark is inferior in the dissipation of charge, while the one which is superior in the dissipation of charge is low in the charge potential. However, this tendency varies with the kind of the charge carrier generating material to be employed and also the kind of the charge transfer material to be employed. It is preferable from the practical viewpoint to choose a suitable combination which is capable of dissipating the charge to such an extent that the background is not stained and attaining a charge potential sufficient to obtain a satisfactory image density.
A multiplicity of charge carrier generating materials have hitherto been proposed. As the particularly effective ones there can be enumerated, for instance, CI Pigment Blue 25 (color index 21180), an azo pigment having a carbazole skeleton (Japanese Laid-open Patent Application No. 95033/1978), an azo pigment having a triphenylamine skeleton (Japanese Laid-open Patent Application No. 132347/1978), an azo pigment having a styrylstilbene skeleton (Japanese Laid-open Patent Application No. 133445/1978), an azo pigment having a diphenyloxadiazole skeleton (Japanese Laid-open Patent Application No. 12742/1979), an azo pigment having a fluorenone skeleton (Japanese Laid-open Patent Application No. 22834/1979) and the like. In this connection, it is to be noted that for the above-mentioned reason, a suitable charge transfer substance should be selected in conformity with a charge carrier generating substance to be employed.